China Geological SurveyHost
Advanced Search
Previous Article Next Article
2022 Vol. 41, No. 7
Article Contents
Article navigation > Geological Bulletin of China > 2022 > 41(7): 1155-1168
Next Article Previous Article

LUO Anbo, FAN Jianjun, ZHANG Bochuan, DUAN Menglong. Discussion on tectonic setting of Upper Jurassic-Lower Cretaceous Shamuluo Formation along Bangong-Nujiang suture zone[J]. Geological Bulletin of China, 2022, 41(7): 1155-1168. doi: 10.12097/j.issn.1671-2552.2022.07.003
Citation: LUO Anbo, FAN Jianjun, ZHANG Bochuan, DUAN Menglong. Discussion on tectonic setting of Upper Jurassic-Lower Cretaceous Shamuluo Formation along Bangong-Nujiang suture zone[J]. Geological Bulletin of China, 2022, 41(7): 1155-1168. doi: 10.12097/j.issn.1671-2552.2022.07.003
shu

Discussion on tectonic setting of Upper Jurassic-Lower Cretaceous Shamuluo Formation along Bangong-Nujiang suture zone

  • 1.

    College of Earth Science, Jilin University, Changchun 130061, Jilin, China

  • 2.

    Key Laboratory of Mineral Resources Evaluation in Northeast Asia, Ministry of Natural Resources, Changchun 130026, Jilin, China

More Information
Received Date:  20 January 2021
Revised Date:  08 April 2021
Publish Date:  15 July 2022
    Abstract

  • The uncertainty of closure of the Bangong-Nujiang ocean has restricted the understanding of the late Mesozoic evolution of the Xizangen Plateau and the Metallogenic Geodynamic background of the Bangong-Nujiang metallogenic belt.The sedimentary unconformity between the Upper Jurassic-Lower Cretaceous Shamuluo Formation and the underlying oceanic crust materials is a key to solve the above problems.In this paper, the chronological and sedimentological characteristics of the Shamuluo Formation are summarized in detail by sorting out the previous research data.Then, we propose that the Upper Jurassic-Lower Cretaceous Shamuluo Formation can be divided into the Late Jurassic-late Early Cretaceous(Oxfordsian-Aptian) shallow marine shelf-slope facies strata and the end of Early Cretaceous(Albian) estuarine-coastal facies strata.On the basis, it is suggested that the lower part and its sedimentary unconformity probably represented arc-arc and arc-continent collisions along the northern margin of the Bangong-Nujiang ocean during the Late Jurassic-Early Cretaceous, while the upper part should be formed in the background of closure of Bangong-Nujiang ocean and subsequent Lhasa-Qiangtang initial soft collision.Therefore, we believe that the middle and western segments of Bangong-Nujiang ocean was not closed until the Albian.

    • FullText(HTML)
  • 加载中
    • References
  • [1] 范建军. 班公湖-怒江洋中西段晚中生代汇聚消亡时空重建[D]. 吉林大学博士学位论文, 2016.

    Google Scholar

    [2] 肖文交, 敖松坚, 杨磊, 等. 喜马拉雅汇聚带结构-属性解剖及印度-欧亚大陆最终拼贴格局[J]. 中国科学: 地球科学, 2017, 47(6): 631-656.

    Google Scholar

    [3] 侯泉林, 郭谦谦, 方爱民. 造山带研究中有关复理石和磨拉石的几个问题[J]. 岩石学报, 2018, 34(7): 1885-1896.

    Google Scholar

    [4] 丁林, Satybaev M A, 蔡福龙, 等. 印度与欧亚大陆初始碰撞时限、封闭方式和过程[J]. 中国科学: 地球科学, 2017, 47(3): 293-309.

    Google Scholar

    [5] Zhu D C, Li S M, Cawood P A, et al. Assembly of the Lhasa and Qiangtang terranes in central Xizang by divergent double subduction[J]. Lithos, 2016, 245(15): 7-17.

    Google Scholar

    [6] 尼玛次仁, 谢尧武, 沙昭礼, 等. 1: 25万那曲县幅地质调查报告[M]. 北京: 地质出版社, 2010.

    Google Scholar

    [7] 郑有业, 何建社, 李维军, 等. 1: 25万兹格塘错幅地质调查报告[M]. 北京: 地质出版社, 2010.

    Google Scholar

    [8] Ma A L, Hu X M, Kapp P, et al. The disappearance of a Late Jurassic remnant sea in the southern Qiangtang Block (Shamuluo Formation, Najiangco area): Implications for the tectonic uplift of central Xizang[J]. Palaeogeography, Palaeoclimatology, Palaeoecology, 2018, 506: 30-47. doi: 10.1016/j.palaeo.2018.06.005

    CrossRef Google Scholar

    [9] 谢国刚, 邹爱建, 袁建芽, 等. 西藏1: 25万邦多幅区域地质调查报告[M]. 北京: 地质出版社, 2010.

    Google Scholar

    [10] 曾庆高, 毛国政, 王保弟, 等. 1: 5万改则县幅等4幅区域地质调查报告[M]. 北京: 地质出版社, 2010.

    Google Scholar

    [11] 纪占胜, 姚建新, 武桂春. 西藏改则县物玛乡北部晚侏罗世吐卡日组珊瑚动物群的发现及其地质意义[J]. 地质通报, 2011, 30(2/3): 418-438.

    Google Scholar

    [12] 陈玉禄, 张宽忠, 勾永东, 等. 1: 25万物玛幅等4幅区域地质调查报告[M]. 北京: 地质出版社, 2010.

    Google Scholar

    [13] 刘文, 吴建亮, 雷传扬, 等. 西藏革吉地区沙木罗组碎屑锆石年代学研究: 物源及其对班公湖-怒江特提斯洋西段闭合时限的制约[J]. 岩石学报, 2019, 35(6): 1738-1756.

    Google Scholar

    [14] 谢国刚, 肖志坚, 欧阳克贵, 等. 西藏1: 25万喀纳幅、日土县幅区域地质调查报告[M]. 北京: 地质出版社, 2010.

    Google Scholar

    [15] Huang T T, Xu J F, Chen J L, et al. Sedimentary record of Jurassic northward subduction of the Bangong-Nujiang ocean: Insights from detrital zircons[J]. International Geology Review, 2016, 59(2): 166-184.

    Google Scholar

    [16] 吴建亮, 刘文, 尹显科, 等. 藏北班公湖-怒江缝合带西段沙木罗组火山岩年代学、Hf同位素及地球化学特征[J]. 地球科学, 2020, 39: 1-26.

    Google Scholar

    [17] 张建珍, 高莲凤, 张振国, 等. 西藏日土早白垩世高镁流纹质岩石时代、地球化学特征及地质意义[J]. 地球科学, 2020, 45(8): 2868-2881.

    Google Scholar

    [18] 樊帅权, 史仁灯, 丁林, 等. 碎屑锆石对班公湖地区晚侏罗世-早白垩世沉积物源的制约[J]. 地质科学, 2011, 46(3): 847-864. doi: 10.3969/j.issn.0563-5020.2011.03.019

    CrossRef Google Scholar

    [19] Li S, Ding L, Guilmette C, et al. The subduction-accretion history of the Bangong-Nujiang ocean: Constraints from provenance and geochronology of the Mesozoic strata near Gaize, central Xizang[J]. Tectonophysics, 2017, 702: 42-60. doi: 10.1016/j.tecto.2017.02.023

    CrossRef Google Scholar

    [20] Li C, Wang G H, Zhao Z B, et al. Late Mesozoic tectonic evolution of the central Bangong-Nujiang Suture Zone, central Xizang Plateau[J]. International Geology Review, 2020, 62(18): 2300-2323. doi: 10.1080/00206814.2019.1697859

    CrossRef Google Scholar

    [21] Xu W, Xu M J, Wu Y W, et al. Petrology geochemistry and geochronology of boninitic dykes from the Kangqiong ophiolite: implications for the Early Cretaceous evolution of Bangong-Nujiang Neo-Tethys Ocean in Xizang[J]. International Geology Review, 2015, 57(16): 2028-2043. doi: 10.1080/00206814.2015.1050464

    CrossRef Google Scholar

    [22] 罗安波, 范建军, 王明, 等. 班公湖-怒江洋复理石沉积时代: 来自改则县亚多村碎屑锆石的制约[J]. 地球科学, 2019, 44(7): 2426-2444.

    Google Scholar

    [23] 耿全如, 彭智敏, 张璋, 等. 班公湖-怒江成矿带及邻区特提斯演化与成矿地质背景[M]. 北京: 地质出版社, 2012.

    Google Scholar

    [24] Li X K, Chen J, Wang R C, et al. Temporal and spatial variations of Late Mesozoic granitoids in the SW Qiangtang, Xizang: Implications for crustal architecture, Meso-Tethyan evolution and regional mineralization[J]. Earth-Science Reviews, 2018, 185: 374-396. doi: 10.1016/j.earscirev.2018.04.005

    CrossRef Google Scholar

    [25] 余光明, 王成善. 西藏特提斯沉积地质[M]. 北京: 地质出版社, 1990.

    Google Scholar

    [26] 陈国荣, 刘鸿飞, 蒋光武, 等. 西藏班公湖-怒江结合带中段沙木罗组的发现[J]. 地质通报, 2004, 23(2): 193-94. doi: 10.3969/j.issn.1671-2552.2004.02.015

    CrossRef Google Scholar

    [27] 谢冰晶, 程捷, 黄传冠. 班公湖-怒江结合带西段沙木罗组的发现及意义[J]. 东华理工大学学报(自然科学版), 2010, 33(2): 159-164. doi: 10.3969/j.issn.1674-3504.2010.02.008

    CrossRef Google Scholar

    [28] Zhu D C, Mo X X, Niu Y L, et al. Geochemical investigation of Early Cretaceous igneous rocks along an east-west traverse throughout the central Lhasa Terrane, Xizang[J]. Chemical Geology, 2009, 268(3/4): 298-312.

    Google Scholar

    [29] Zhu D C, Zhao Z D, Niu Y L, et al. The Lhasa Terrane: record of a microcontinent and its histories of drift and growth[J]. Earth and Planetary Science Letters, 2011, 301(1/2): 241-255.

    Google Scholar

    [30] 常青松, 朱弟成, 赵志丹, 等. 西藏羌塘南缘热那错早白垩世流纹岩锆石U-Pb年代学和Hf同位素及其意义[J]. 岩石学报, 2011, 27(7): 2034-2044.

    Google Scholar

    [31] Chen Y, Zhu D C, Zhao Z D, et al. Slab break off triggered ca 113 Ma magmatism aroud Xainza area of the Lhasa Terrane Xizang[J]. Gondwana Research, 2014, 26(2): 449-463. doi: 10.1016/j.gr.2013.06.005

    CrossRef Google Scholar

    [32] 丁林, 来庆洲. 冈底斯地壳碰撞前增厚及隆升的地质证据: 岛弧拼贴对青藏高原隆升及扩展历史的制约[J]. 科学通报, 2003, 48(8): 836-842. doi: 10.3321/j.issn:0023-074X.2003.08.018

    CrossRef Google Scholar

    [33] Chen S S, Shi R D, Gong X H, et al. A syn-collisional model for Early Cretaceous magmatism in the northern and central Lhasa subterranes[J]. Gondwana Research, 2017, 41: 93-109. doi: 10.1016/j.gr.2015.04.008

    CrossRef Google Scholar

    [34] Hu P Y, Zhai Q G, Jahn B M, et al. Late Early Cretaceous magmatic rocks (118-113 Ma) in the middle segment of the Bangong-Nujiang suture zone, Xizang Plateau: evidence of lithospheric delamination[J]. Gondwana Research, 2017, 44: 116-138. doi: 10.1016/j.gr.2016.12.005

    CrossRef Google Scholar

    [35] Li X K, Chen J, Wang R C, et al. Early Cretaceous tectonomagmatic evolution and basin development of western Bangong-Nujiang suture: A complete history of soft collision[J]. Lithos, 2019, 360-373.

    Google Scholar

    [36] Zhang K J, Xia B D, Wang G M, et al. Early Cretaceous stratigraphy, depositional environments, sandstone provenance, and tectonic setting of central Xizang, western China[J]. Geological Society of America Bulletin, 2004, 116(9): 1202-1222. doi: 10.1130/B25388.1

    CrossRef Google Scholar

    [37] 王忠恒, 王永胜, 谢元和, 等. 西藏班公湖-怒江缝合带中段塔仁本洋岛型玄武岩的发现及地质意义[J]. 沉积与特提斯地质, 2005, 25(1/2): 155-162.

    Google Scholar

    [38] 朱弟成, 潘桂棠, 莫宣学, 等. 青藏高原中部中生代OIB型玄武岩的识别: 年代学、地球化学及其构造环境[J]. 地质学报, 2006, 80(9): 1312-1328. doi: 10.3321/j.issn:0001-5717.2006.09.008

    CrossRef Google Scholar

    [39] Zhang K J, Xia B, Zhang Y X, et al. Central Xizang Meso-Tethyan oceanic plateau[J]. Lithos, 2014, 210/211: 278-288. doi: 10.1016/j.lithos.2014.09.004

    CrossRef Google Scholar

    [40] Fan J J, Li C, Xue C M, et al. Petrology geochemistry and geochronology of the Zhonggang ocean island northern Tiber: implications for the evolution of the Bangongco-Nujiang oceanic arm of Neo-Tethys[J]. International Geology Review, 2014, 56(12): 1504-1520. doi: 10.1080/00206814.2014.947639

    CrossRef Google Scholar

    [41] Fan J J, Niu Y L, Liu Y M, et al. Timing of closure of the Meso-Tethys Ocean: Constraints from remnants of a 141-135 Ma ocean island within the Bangong-Nujiang Suture Zone, Xizang Plateau[J]. Geological Society of America Bulletin, 2021, 133(9/10): 1875-1889.

    Google Scholar

    [42] 刘庆宏, 肖志坚, 曹圣华, 等. 班公湖-怒江结合带西段多岛弧盆系时空结构初步分析[J]. 沉积与特提斯地质, 2004, 24(3): 15-21.

    Google Scholar

    [43] Zhang K J, Zhang Y X, Tang X C, et al. Late Mesozoic tectonic evolution and growth of the Xizang Plateau prior to the Indo-Asian collision[J]. Earth Science Reviews, 2012, 114(3/4): 236-249.

    Google Scholar

    [44] Fan J J, Li C, Xie C M, et al. The evolution of the Bangong-Nujiang Neo-Tethys ocean: Evidence from zircon U-Pb and Lu-Hf isotopic analyses of Early Cretaceous oceanic islands and ophiolites[J]. Tectonophysics, 2015, 655(1): 27-40.

    Google Scholar

    [45] Zhang Y X, Li Z W, Yang W G, et al. Late Jurassic-Early Cretaceous episodic development of the Bangong Meso-Tethyan subduction: Evidence from elemental and Sr-Nd isotopic geochemistry of arc magmatic rocks, Gaize region, central Xizang, China[J]. Journal of Asian Earth Sciences, 2017, 135: 212-242. doi: 10.1016/j.jseaes.2016.12.043

    CrossRef Google Scholar

    [46] Li S M, Wang Q, Zhu D C, et al. Reconciling Orogenic Drivers for the Evolution of the Bangong-Nujiang Tethys During Middle-Late Jurassic[J]. Tectonics, 2020, 39: e2019TC005951.

    Google Scholar

    [47] Cao M J, Qin K Z, Li G M, et al. Tectono-magmatic evolution of Late Jurassic to Early Cretaceous granitoids in the west central Lhasa subterrane, Xizang[J]. Gondwana Research, 2016, 39: 386-400.

    Google Scholar

    [48] Li J X, Qin K Z, Li G M, et al. Geochronology geochemistry and zircon Hf isotopic compositions of Mesozoic intermediate-felsic intrusions in central Xizang: Petrogenetic and tectonic implications[J]. Lithos, 2014, 198/199: 77-91.

    Google Scholar

    [49] Wang W, Wang M, Zhai Q G, et al. Transition from oceanic subduction to continental collision recorded in the Bangong-Nujiang suture zone: Insights from Early Cretaceous magmatic rocks in the north-central Xizang[J]. Gondwana Research, 2020, 78: 77-91.

    Google Scholar

    [50] Xu W, Li C, Wang M, et al. Subduction of a spreading ridge within the Bangong Co-Nujiang Tethys Ocean: Evidence from Early Cretaeous mafic dykes in the Duolong porphyry Cu-Au deposit, western Xizang[J]. Gondwana Research, 2017, 41: 128-141.

    Google Scholar

    [51] 范建军, 李才, 王明, 等. 班公湖-怒江缝合带洞错混杂岩物质组成、时代及其意义[J]. 地质通报, 2018, 37(8): 1417-1427.

    Google Scholar

    [52] Allègre C J, Courtillot V, Tapponnier P, et al. Structure and evolution of the Himalaya-Xizang orogenic belt[J]. Nature, 1984, 307: 17-22.

    Google Scholar

    [53] 李才, 黄小鹏, 翟庆国, 等. 龙木错-双湖-吉塘板块缝合带与青藏高原冈瓦纳北界[J]. 地学前缘, 2006, 13(4): 136-147.

    Google Scholar

    [54] 潘桂棠, 陈智梁, 李兴振, 等. 东特提斯地质构造形成演化[M]. 北京: 地质出版社, 1997.

    Google Scholar

    [55] 范建军, 李兴奎, 张天羽, 等. 班公湖-怒江洋中西段汇聚消亡时空重建[M]. 北京: 地质出版社, 2017.

    Google Scholar

    [56] Girardeau J, Marcoux J, Allegre C J, et al. Tectonic environment and geodynamic significance of the Neo-Cimmerian Dongqiao ophiolite, Bangong-Nujiang suture zone, Xizang[J]. Nature, 1984, 307: 27-31.

    Google Scholar

    [57] Shi R D, Yang J S, Xu Z Q, et al. The Bangong Lake ophiolite (NW Xizang) and its bearing on the tectonic evolution of the Bangong-Nujiang suture zone[J]. Journal of Asian Earth Sciences, 2008, 32: 438-457.

    Google Scholar

    [58] Fan J J, Li C, Wang M, et al. Remnants of a Late Triassic ocean island in the Gufeng area, northern Xizang: implications for the opening and early evolution of the Bangong-Nujiang Tethyan Ocean[J]. Journal of Asian Earth Sciences, 2017, 135: 35-50.

    Google Scholar

    [59] Fan J J, Li C, Liu J H, et al. The Middle Triassic evolution of the Bangong-Nujiang Tethyan Ocean: Evidence from analyses of OIB-type basalts and OIB-derived phonolites in northern Xizang[J]. International Journal of Earth Sciences, 2018, 107: 1755-1775.

    Google Scholar

    [60] 潘桂棠, 莫宣学, 侯增谦, 等. 冈底斯造山带的时空结构及演化[J]. 岩石学报, 2006, 22(3): 521-533.

    Google Scholar

    [61] 西藏自治区地质矿产局. 西藏自治区区域地质志[M]. 北京: 地质出版社, 1993.

    Google Scholar

    [62] 曹圣华, 肖晓琳, 欧阳克贵. 班公湖-怒江结合带西段侏罗纪木嘎岗日群的重新厘定及意义[J]. 沉积学报, 2008, 26(4): 559-564.

    Google Scholar

    [63] 陈顺. 西藏班公湖-怒江带西段改则地区木嘎岗日岩群物质组成及构造意义[D]. 成都理工大学硕士学位论文, 2015.

    Google Scholar

    [64] Luo A B, Fan J J, Hao Y J, et al. Aptian Flysch in Central Xizang: Constraints on the Timing of Closure of the Bangong-Nujiang Tethyan Ocean[J]. Tectonics, 2020, 39, e2020TC006198.

    Google Scholar

    [65] 谌微微. 羌塘地块白垩纪火山岩和红层古地磁学和年代学新结构及其大地构造意义[D]. 中国地质大学博士学位论文, 2014.

    Google Scholar

    [66] 吴浩, 李才, 胡培远, 等. 西藏尼玛县塔色普勒地区去申拉组火山岩的发现及其地质意义[J]. 地质通报, 2013, 32(7): 1014-1026.

    Google Scholar

    [67] 王立全, 潘桂棠, 丁俊, 等. 青藏高原及邻区地质图及说明书[M]. 北京: 地质出版社, 2013.

    Google Scholar

    [68] 夏代祥, 刘世坤. 西藏自治区岩石地层[M]. 武汉: 中国地质大学出版社, 1997.

    Google Scholar

    [69] Dickinson W R, Gehrels G E. Use of U-Pb ages of detrital zircons to infer maximum depositional ages of strata: A test against a Colorado Plateau Mesozoic database[J]. Earth and Planetary Science Letters, 2009, 288: 115-125.

    Google Scholar

    [70] Wu F Y, Ji W Q, Liu C Z, et al. Detrital zircon U-Pb and Hf isotopic data from the Xigaze fore-arc basin; Constraints on Transhimalayan magmatic evolution in southern Xizang[J]. Chemical Geology, 2010, 271(1/2): 13-25.

    Google Scholar

    [71] 王永胜, 张树岐, 谢元和, 等. 1: 25万昂达尔错幅等4幅区域地质调查报告[M]. 北京: 地质出版社, 2010.

    Google Scholar

    [72] Cawood P A, Hawkesworth C J, Dhuime B. Detrital zircon record and tectonic setting[J]. Geology, 2012, 40(10): 875-878.

    Google Scholar

    [73] Najman Y. The detrital record of orogenesis: A review of approaches and techniques used in the Himalayan sedimentary basins[J]. Earth Science Reviews, 2006, 74: 1-72.

    Google Scholar

    [74] Liu D L, Huang Q S, Fan S Q, et al. Subduction of the Bangong-Nujiang Ocean: constraints from granites in the Bangong Co area, Xizang[J]. Geological Journal, 2014, 49: 188-206.

    Google Scholar

    [75] Zeng Y C, Chen J L, Xu J F, et al. Sediment melting during subduction initiation: geochronological and geochemical evidence from the Darutso high-Mg andesites within ophiolite melange, central Xizang[J]. Geochemistry Geophysics Geosystems, 2016, 17(12): 4859-4877.

    Google Scholar

    [76] 范建军, 张博川, 刘海永, 等. 班公湖-怒江洋早-中侏罗世洋内俯冲: 来自洞错蛇绿岩的证据[J]. 岩石学报, 2019, 35(10): 3048-3064.

    Google Scholar

    [77] Yan L L, Zhang K J. Infant intra-oceanic arc magmatism due to initial subduction induced by oceanic plateau accretion: A case study of the Bangong Meso-Tethys, central Xizang, western China[J]. Gondwana Research, 2020, 79: 110-124.

    Google Scholar

    [78] 傅焓埔, 胡修棉, Erica M C, 等. 西藏雅鲁藏布缝合带甲查拉组: 晚白垩世新特提斯洋海沟沉积?[J]. 中国科学: 地球科学, 2018, 48(10): 1275-1292.

    Google Scholar

    [79] 钱信禹, 戴紧根, 王成善, 等. 藏南柳区砾岩的沉积环境及物源分析: 对雅鲁藏布缝合带古近纪隆升的约束[J]. 岩石学报, 2015, 31(5): 1313-1326.

    Google Scholar

    [80] Soesoo A, Bons P D, Gray D R, et al. Divergent double subduction: tectonic and petrologic consequences[J]. Geology, 1997, 25: 755-758.

    Google Scholar

    [81] 吴建亮, 尹显科, 王波, 等. 藏北阿翁错地区中基性脉岩年代学、地球化学特征及其板内伸展构造作用[J]. 中国地质, 2019, 46(6): 1356-1371.

    Google Scholar

    [82] 雷传扬, 吴建亮, 尹显科, 等. 班公湖-怒江缝合带西段沙木罗组地层中闪长玢岩脉的发现及其地质意义[J]. 矿物岩石地球化学通报, 2018, 37(2): 250-259.

    Google Scholar

    [83] Luo A B, Fan J J, Sun D Y, et al. Terminal stage of divergent double subduction: Insights from Early Cretaceous magmatic rocks in the Gerze area, central Xizang[J]. Lithos, 2022, 420/421: 106713.

    Google Scholar

    ① 西藏区调队. 1∶100万日土幅区域地质调查报告. 1987.

    Google Scholar

    • Relative Articles
  • Cited by
  • Supplements
    • Proportional views
  • 加载中
通讯作者: 陈斌, bchen63@163.com
  • 1. 

    沈阳化工大学材料科学与工程学院 沈阳 110142

  1. 本站搜索
  2. 百度学术搜索
  3. 万方数据库搜索
  4. CNKI搜索

Figures(6)

Export Citation
PDF
XML

Article Metrics

Article views(1780) PDF downloads(276) Cited by(0)

Access History

Other Articles By Authors

Catalog

    /

    DownLoad:  Full-Size Img  PowerPoint
    Return
    版权所有：中国地质调查局发展研究中心 copyright @2020